The present invention represents an improvement upon the drilling method and apparatus of U.S. Pat. No. Re. 26,975, which is assigned to applicant's assignee herein. The disclosure of U.S. Pat. No. Re. 26,975 is hereby incorporated in this application by reference. Briefly, it was found that the cutting efficiency and tool life of a conventional oil hole drill in which coolant is supplied to the drill tip through the interior of the drill is significantly improved by regularly varying the pressure, or pulsing, the coolant fluid supplied to the drill. By so pulsing the flow, such as through regular pulsations of 50 times a minute, tool life was increased by approximately 50%, with feed rates also substantially increased.
Although electric as well as pneumatic motor hydraulic pumps are disclosed in the above identified patent for supplying the coolant to the oil hole drill in a pulsating manner, pneumatic motor driven pumps have generally been found to be most advantageous due to their relatively inexpensive operation and longevity under adverse operating conditions. Additionally, most machine shops have air pressure available in the form of a 90 psi pressure line running throughout the shop for driving small pneumatic motors, such as for portable hand tools so that the power source for a pneumatic pump is generally less expensive and thus far preferred.
It has been observed that the chips created during the drilling operation in the practice of the process disclosed in the above identified patent periodically build-up, become impacted and create a back pressure to the flow of pulsed fluid through the drill. The build-up of back pressure can significantly decrease the rate and therefore the volume of coolant fluid flowing through the drill, resulting in a slower drilling operation and a decrease in the efficiency of the drill. One possible solution to this problem would be to substitute a high pressure volume pulsed flow coolant pump, but for many applications, such a pump operable off of standard shop pressure air lines is not currently commercially available, and the building of a special pump is not economically justified.
It has therefore been one object of this invention to provide an improved method and apparatus for supplying coolant to a drilling tool which minimizes or eliminates chip build-up and impaction at the tool tip. A more specific object has been to provide a coolant supply system for cooling a drill and workpiece during a drilling operation which alleviates the build-up of back pressure to a principal coolant flow caused by chip impaction, etc.
Yet another object of the invention has been to provide a system having a continuous and high volume pulsed flow of coolant to an oil hole drill engaging a workpiece and an intermittant booster high pressure coolant flow which is also pulsed so as to prevent chip build-up at the tool tip.
Yet a further object has been to provide a system for relieving the build-up of back pressure to a continuous and high volume pulsed coolant flow supplied to the drill tip through the interior of the drill employing pneumatically driven pumps.